Sealing Sleeve for Slip Joint

ABSTRACT

A sleeve for sealing an annular gap between opposed co-axial surfaces of a slip joint includes a tubular body formed from a metallic material and having a first end, a second end, a center section between the first and second ends, and a longitudinal cross-sectional profile having a plurality of bendable curves. The sleeve is shaped so that two or more of the bendable curves contact each opposed coaxial surface to form two or more circumferential lines of contact with each opposed coaxial surface. The sleeve further includes a self-protective oxide undercoat layer that protects the metallic material and a lubricous overcoat layer that provides lubricity to the contact surfaces when the sleeve is exposed to temperatures greater than about 600° C.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 61/905,016, filed Nov. 15, 2013, which is incorporated by reference in its entirety herein, and for all purposes.

TECHNICAL FIELD

This disclosure relates generally to sealing sleeves for slip joints, and more specifically to sleeves for sealing the high temperature slip joints found in the exhaust manifolds of large internal combustion engines.

BACKGROUND

The temperature of the exhaust manifolds on large internal combustion engines, and especially on large diesel engines such as class 8 truck engines, can often be much hotter than the head of the engine to which they are attached. As a result, an exhaust manifold can often experience greater thermal expansion than the head, and must be therefore be formed into two or three sections that fit together with sealable slip joints having opposing cylindrical surfaces that slide relative to each other in order to accommodate the thermally-induced growth and shrinkage.

These slip joints can be problematic to keep sealed because of the general lack of a sliding seal mechanism that has durability at such high temperatures. For example, many slip-joints have straight, smooth bores that are machined to close tolerance and initially leak exhaust gasses until they become clogged with carbon build-up. As such, these slip joints never completely seal, but can offer at least some resistance to escaping gases. Another type of exhaust manifold slip joint includes multiple bushings or “C” ring seals that are similar to piston rings, and that are generally mounted within grooves formed into the inner or male cylindrical surface, and with the outer surfaces of the rings being in close proximity to the outer or female cylindrical surface. As the high-temperature environment precludes any liquid sealing lubrication along the opposite surface, these slip joints are subject to leakage as well as galling or binding at the outer edges of the rings if the rings become cocked within their grooves or if the opposing cylindrical surfaces become laterally or angularly misaligned.

Consequently, a need exists for a slip joint that can provide improved sealing while maintaining free movement between the opposing cylindrical surfaces of the joint to accommodate the thermally-induced growth and shrinkage between the parts of the exhaust manifold. The slip joint should also accommodate nominal amounts of lateral or angular misalignment between the different sections of the exhaust manifold. It is toward such a slip joint that the present disclosure is directed.

SUMMARY

In accordance with one embodiment of the present disclosure, a sleeve for sealing an annular gap between the opposed co-axial surfaces of a slip joint generally includes a tubular body formed from a metallic material and having a first end, a second end, a center section between the first and second ends, and a longitudinal cross-sectional profile formed with a plurality of bendable curves. The sleeve is shaped so that two or more bendable curves contact each opposed coaxial surface to form two or more circumferential lines of contact with each opposed coaxial surface. The sleeve also includes an undercoat layer comprising a self-protective oxide coating and that covers substantially all of the surface area of the tubular body, and an overcoat layer that covers the undercoat layer at least about the lines of contact, and which is configured to provide lubricity to the contact surfaces when the sleeve is exposed to temperatures greater than about 600° C. In one aspect, the sleeve is shaped so that a non-flexed distance between opposing circumferential lines of contact, as measured perpendicular to the longitudinal axis of the tubular body, is between about 6% and about 14% greater than an average distance between the opposed coaxial surfaces.

Another embodiment of the sleeve includes a tubular body having a first rolled end, a second rolled end, and a center section between the first and second rolled ends. The first and second rolled ends form inwardly opposing arcs, with each arc having an arc length that is greater than or about 230 degrees to form circumferential lines of contact with each opposed coaxial surface, and an arc diameter in a non-flexed condition that is about 10% or greater than an average distance between the opposed coaxial surfaces. In addition, the center section is spaced from a nearest slip joint surface by at least 10% of the average distance between the opposed coaxial surfaces upon installation of the sleeve into the annular gap.

Yet another embodiment of the sleeve includes a tubular body formed from a metallic material and having a first end, a second end, and a center section between the first and second ends, with the center section having a bendable wave-shaped profile that includes a plurality of alternating peaks that alternately contact the opposed co-axial surfaces. At least two peaks contact each opposed coaxial surface to form at least two circumferential lines of contact with each opposed coaxial surface. The sleeve also includes an undercoat layer comprising a self-protective oxide coating that covers substantially all of the surface area of the tubular body, and an overcoat layer that covers the undercoat layer at least on each of the peaks of the wave-shaped profile, and which is configured to provide lubricity to the contact surfaces when the sleeve is exposed to temperatures greater than about 600° C. In one aspect the sleeve includes a non-flexed amplitude, as measured between the lines of contact of adjacent opposing peaks, that is about 10% or greater than an average distance between the opposed coaxial surfaces.

Another embodiment of the disclosure comprises a high temperature slip joint for a separable exhaust manifold that includes a substantially smooth outer cylindrical surface formed on a first section of the exhaust manifold, a substantially smooth inner cylindrical surface formed on a second section of the exhaust manifold, with at least a portion of the inner cylindrical surface being radially spaced from the outer cylindrical surface when the first and second sections of the exhaust manifold are coupled to an engine. The slip joint further includes a sealing sleeve disposed between the outer cylindrical surface and the inner cylindrical surface, which sealing sleeve generally comprises a tubular body formed from a metallic material and having a longitudinal cross-sectional profile that includes a plurality of bendable curves or peaks. Two or more of the bendable curves contact each of the inner and outer cylindrical surfaces, respectively, to form two or more circumferential lines of contact on each surface that operate to establish a slidable seal which restricts the passage of hot exhaust gases between the inside of the exhaust manifold and ambience.

The sleeve also includes an undercoat layer comprising a self-protective oxide coating that covers substantially all of the surface area of the tubular body, and an overcoat layer on the undercoat layer that is configured to provide lubricity to the surfaces that contact outer and inner cylindrical surfaces when the slip joint is exposed to temperatures greater than about 600° C.

The invention will be better understood upon review of the detailed description set forth below taken in conjunction with the accompanying drawing figures, which are briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective side view of a split or separable exhaust manifold having a cylindrical slip joint, as found in the prior art.

FIG. 2 is a perspective view of the prior art cylindrical slip joint of FIG. 1.

FIG. 3 is a perspective side view of a high temperature slip joint, in accordance with a representative embodiment of the present disclosure.

FIG. 4 is a perspective side view of the exhaust manifold sections of the slip joint of FIG. 3 without a sealing sleeve.

FIG. 5 is a perspective view of the sealing sleeve of the high temperature slip joint of FIG. 3.

FIG. 6 is an exaggerated cross-sectional view of the sealing sleeve of FIG. 5.

FIG. 7 is a cross-sectional view of the assembled slip joint of FIG. 3.

FIG. 8 is an expanded cross-sectional view of the assembled slip joint of FIG. 3.

FIG. 9 is a perspective view of a sealing sleeve for a high temperature slip joint, in accordance with another representative embodiment.

FIG. 10 is a cross-sectional perspective view of the sealing sleeve of FIG. 9.

FIG. 11 is a close-up cross-sectional view of the sealing sleeve of FIG. 9 that has been installed between the exhaust manifold sections of a slip joint.

FIG. 12 is a close-up cross-sectional view of a portion of the installed sealing sleeve of FIG. 11.

FIG. 13 is an exploded cross-sectional view of a slip joint that includes the sealing sleeve of FIG. 9, in accordance with another representative embodiment.

FIG. 14 is a cross-sectional perspective view of the slip joint of FIG. 13 during installation of the sealing sleeve between the exhaust manifold sections.

FIG. 15 is a cross-sectional view of the assembled slip joint of FIG. 13.

FIG. 16 is a close up, cross-sectional view of the assembled slip joint of FIG. 13.

Those skilled in the art will appreciate and understand that, according to common practice, various features of the drawings discussed below are not necessarily drawn to scale, and that dimensions of various features and elements of the drawings may be expanded or reduced to more clearly illustrate the embodiments of the present invention described herein.

DETAILED DESCRIPTION

Referring now in more detail to the drawing figures, wherein like parts are identified with like reference numerals throughout the several views, FIGS. 1-2 together illustrate a split or separable exhaust manifold 10 that is mounted to a large engine, such as a class 8 truck diesel engine, and configured to receive and direction the hot exhaust gases therefrom toward an exhaust system. As shown, the separable exhaust manifold 10 generally includes a first section 20 having a tubular attachment end 22 that is slidably engageable within the tubular attachment end 32 of a second section 30 to form a slip joint 50. The tubular attachment ends 22, 32 are slidably engageable with each other at the slip joint 50 so as to contain and control the flow of hot exhaust gases while accommodating the thermally-induced growth and shrinkage of the first section 20 and second section 30 of the exhaust manifold 10 as the sections 20, 30 expand during operation of the hot engine, and afterward axially contract in a cooling state. The exhaust manifold 10 shown in FIGS. 1-2 only includes one slip joint 50. However, other exhaust manifolds for large engines may include two or more slip joints disposed along the length thereof, as desired.

As further shown in the close-up view of FIG. 2, the prior art slip joint 50 of the separable exhaust manifold 10 can have a generally cylindrical configuration with an inner or male cylindrical surface 24 formed into the tubular attachment end 22 of the first section 20, and a bore 34 having an outer or female cylindrical surface 36 formed into the tubular attachment end 32 of the second section 30, with the inner cylindrical surface 24 being substantially co-axial with and radially spaced from the outer cylindrical surface 36 when the first and second sections of the exhaust manifold 10 are assembled together and coupled to an engine. The illustrated prior art slip joint 50 further includes multiple bushings or “C” ring seals that are similar to piston rings (not shown), and that are mounted within grooves 26 formed into the inner or male cylindrical surface 24, and with the outer surfaces of the rings being in close proximity to the outer or female cylindrical surface 36 of the bore 34. As discussed above, prior art slip joints, such as the type of slip joint 50 shown in FIGS. 1-2, can have suffer from numerous deficiencies in maintaining an adequate seal that prevents the leakage of exhaust gases to ambience.

In accordance with a representative embodiment of the present disclosure, illustrated in FIGS. 3-8 is a high temperature slip joint 150 for a split or separable exhaust manifold 110 that can overcome many of these deficiencies to provide improved sealing around the circumference of the slip joint 150. The slip joint 150 can maintain the seal while allowing for substantially free axial movement between the opposing cylindrical surfaces of the joint, so as to accommodate the thermally-induced growth and shrinkage between the various sections 120, 130 of the exhaust manifold 110. In addition, the slip joint 150 can provide a degree of geometric robustness in maintaining the seal while accommodating a predetermined amount of radial and/or angular misalignment between the inner and outer cylindrical surfaces of the joint 150.

As shown in FIGS. 3 and 4, the high temperature slip joint 150 can include a sealing sleeve 140 having a wave-shaped cross-sectional profile, that can be installed over the inner or male cylindrical surface 124 formed into the tubular attachment end 122 of the first section 120. To assemble the exhaust manifold 110, the inner cylindrical surface 124 and installed sealing sleeve 140 can then be inserted into the bore 134 formed into the tubular attachment end 132 of the second section 130. Accordingly, the outer cylindrical surface 136 is radially spaced from the inner cylindrical surface 124 when the engaged sections 120, 130 of the exhaust manifold 110 are coupled to an engine, with the sealing sleeve 140 being disposed between the substantially co-axial cylindrical surfaces 124, 136 (FIGS. 7-8). Both the inner cylindrical surface 124 and the outer cylindrical surface 136 generally have substantially smooth surface finishes so that the alternating peaks of the wave-shaped sealing sleeve 140 can form substantially continuous lines of contact around the entire circumference of the sealing sleeve.

As shown in FIG. 4, in one aspect the inner or male cylindrical surface 124 and the outer or female cylindrical surface 136 can be concentric or co-axial, in which the centerline axis 121 of the inner cylindrical surface 124 is substantially aligned with the centerline axis 131 of the outer cylindrical surface 136. In other aspects, however, centerline axis 121 may not be aligned with the centerline axis 131. Instead, for example, the centerline axis 121A may be displaced from a true position 121 by a lateral misalignment offset 125, or centerline axis 131A may be inclined from a true orientation 131 by an angular misalignment offset 135. Nevertheless, in a preferred embodiment the sealing sleeve 140 (FIG. 3) can provide the high temperature slip joint 150 with the ability to maintain a seal between the inner cylindrical surface 124 and the outer cylindrical surface 136 up to and including a predetermined about of lateral offset 125 and/or angular offset 135.

With reference to FIG. 5, in one aspect the sealing sleeve 140 can include a high-temperature metallic substrate 142 that has been roll-corrugated and laser welded to a particular size to form a wave-shaped tubular body having a plurality of alternating peaks 146 separated by valleys 148. The substrate 142 can subsequently be provided with a high temperature undercoat 143 and a low friction overcoat 145 (FIG. 6). As a result, the outermost contact surfaces of the alternating peaks 146 of the sealing sleeve 140 can be configured to contact and slide along the inner 124 and outer 136 cylindrical surfaces (FIG. 3) formed into the tubular attachment ends 122, 132 of the split exhaust manifold sections 120, 130, respectively, to provide multiple circumferential lines of contact along each cylindrical surface that restrict the passage of hot gases passing through the seal 150 on both the inner and outer sides of the sealing sleeve 140.

As described above, the tubular body or substrate 142 of the sealing sleeve 140 can be formed from a stiff but bendable metallic material, such as a stainless steel alloy, an, and a high-nickel alloy, that maintains its bulk material properties at high temperatures greater than 600° C. While stainless steel alloys, and especially ferric stainless steel alloys, may be considered a preferred embodiment, the substrate may also be formed from other high temperature-resistant metals, such as an Inconel alloy or alloys having a high-aluminum, high-nickel or high-titanium content.

The tubular body or substrate 142 includes an upper surface, a lower surface, and edges at both ends, and in one aspect can be seamless or formed with a seamless construction. Generally, substantially all of the surface area of the substrate 142, including both the upper and lower surfaces and the end edges, is covered with a first layer or undercoat 143 comprising a self-protective oxide coating that provides protection from oxidation corrosion at high temperatures. As discussed in more detail below, the self-protective oxide coating 143 can be formed through the application of a plurality of nanoparticles to the surfaces of the substrate 142, which is then heated to a first elevated temperature and for a predetermined period of time to form the self-protective oxide coating 143.

After the formation of the self-protective oxide coating 143, a low-friction second layer or overcoat 145 can be applied to the undercoat layer 143 to provide lubricity to the contact surfaces of the sealing sleeve 140 even when the sealing sleeve is exposed to the elevated temperatures experienced by the exhaust manifold, which can often reach and exceed 600° C. In one aspect the low-friction overcoat 145 can comprise boron nitride.

Further to the above, the first layer or undercoat 143 can comprise a protective coating that is formed from a plurality of nanoparticles that have been applied in a solution or suspension (more accurately referred to hereinafter as a “nanoparticle suspension”, or “suspension”) to the surfaces (and edges) of the tubular body or substrate 142. The suspension can be rolled, sprayed or brushed onto the substrate, or the substrate 142 can be dip coated into the suspension. In one aspect, a single application of the nanoparticle suspension can generally be sufficient to deposit the desired amount of nanoparticles onto the surfaces of the substrate 142. However, in other aspects the nanoparticle suspension can be applied and dried multiple times until the materials deposited onto the surface of the substrate have reach their desired coverage and concentration, with the substrate being air dried at ambient temperature or heat dried at a temperature that is generally less than 100° C. The substrate 142 and the applied nanoparticles can then be heated together to a first elevated temperature and for a predetermined period of time to form the protective undercoat 143 that resists the severe oxidation corrosion that would otherwise occur on the surfaces of the tubular body or substrate 142.

In one aspect, the average size of the nanoparticles can be 50 nanometers or less. In other aspects, the average size of the nanoparticles can be 20 nanometers or less, or even 10 nanometers or less. Furthermore, the nanoparticles can generally be oxides of an element, including but not limited to cerium oxide nanoparticles, titanium oxide nanoparticles, aluminum oxide nanoparticles, silicon oxide nanoparticles, scandium oxide nanoparticles, yttrium oxide nanoparticles, zirconium oxide nanoparticles, niobium oxide nanoparticles, hafnium oxide nanoparticles, tantalum oxide nanoparticles, and thorium oxide.

In one embodiment of the present disclosure, the individual nanoparticles can be broadly scattered or dispersed over the surfaces of the tubular body or substrate 142, without forming a continuous layer. The dispersed and scattered nanoparticles can then interact with the base alloy material of the substrate 142 during heating to the first elevated temperature to form the thin, self-protective oxide coating 143. The oxide coating 143 grows or forms to cover the surfaces of the substrate substantially completely, as described in U.S. Pat. No. 8,197,613, which issued on Jun. 12, 2012. This patent is incorporated by reference in its entirely herein and for all purposes.

Without being bound to any particular mechanism or theory, it is contemplated that the nanoparticles that are scattered and dispersed over the surface of the substrate serve as nucleation sites for the development and growth of a fine-grained, uniform, and stable thermal oxide coating 143 that forms as a result of oxidation of the base alloy during the heating process. In one aspect, the first elevated temperature can be greater than or about 600° C. and for a period ranging from about one minute to about forty-eight hours. In yet another aspect, the first elevated temperature can be greater than or about 800° C. and for a period ranging from about one minute to about forty-eight hours.

Alternatively, through experimentation and practice it has been discovered that it may also be possible to form the self-protective oxide coating at temperatures far below those elevated temperatures that were previously considered. For instance, and again without being bound to any particular mechanism or theory, it is also contemplated that the substrate may only require heating to a temperature as low as 200° C., or even to temperatures as low as 80° C. to 100° C., to form the thin, self-protective oxide coating 143. Thus, in one representative embodiment the first elevated temperature for forming the self-protective oxide coating, or undercoat layer, can range between about 80° C. and about 600° C., while in another embodiment the first elevated temperature can range between about 80° C. and about 200° C., and in yet another embodiment the first elevated temperature can range between about 80° C. and about 100° C. In the above embodiments, the substrate coated in the nanoparticle solution can be maintained at the first elevated temperature for a period of time ranging from about five minutes to about thirty minutes, with a preferred period of time being nearer the shorter end of the range, or about five minutes, so as to reduce the time and cost needed to form the self-protective oxide coating during manufacturing.

The suspension of nanoparticles used to form the first layer or undercoat 143 can include the nanoparticles suspended in a volatile carrier fluid, such as toluene, that can be readily evaporated at room temperature to deposit the nanoparticles onto the surfaces of the substrate 142. In this embodiment the carrier fluid can simply evaporate or burn off during the heating step that forms the protective undercoat.

In other embodiments the carrier fluid can comprise a mixture of water and a surfactant, such as soap, that can leave a residue on the substrate during the heating step used to create the protective undercoat. As the surfactant residue can affect the bonding between the protective undercoat layer and the lubricious overcoat layer, the residue can be removed from the substrate by washing the substrate to remove the residue prior to applying the second layer or overcoat 145 over the undercoat 143. In one aspect, the substrate can be washed in an ultra-sonic parts washer filled with clean water or other cleanser, and then dried prior to the application of the overcoat 145.

After the first layer or undercoat 143 has been formed over the surfaces of the tubular body or substrate 142 through the application and heating of nanoparticles, a second layer or overcoat 145 can be applied over the undercoat 143 to provide lubricity and sealability to the surfaces of the sealing sleeve 140 when the sealing sleeve is exposed to temperatures greater than about 600° C. In one aspect of the present disclosure, the anti-friction or lubricious overcoat 145 can comprise boron nitride, which can be applied over substantially all of the surface area of the undercoat 143, or which may be limited in application to the raised contact surfaces 149 of any bendable peaks or curves 146 which may be formed into the longitudinal cross-sectional profile of the substrate 142.

As with the nanoparticle solution, the overcoat 145 can be applied to the surfaces of the substrate 142 as a liquid, such as a solution comprising boron nitride, which can be rolled, sprayed or brushed onto the substrate, or into which the substrate 142 can be dip coated. After application, the liquid overcoat can then be heat dried at a second elevated temperature that can range, in one aspect, between about 80° C. and about 200° C. In another aspect, the second elevated temperature can range between about 80° C. and about 100° C. The substrate with the self-protective undercoat layer 143 that is coated, at least in part, with the overcoat layer can be maintained at the second elevated temperature for a period of time ranging from about five minutes to about thirty minutes, with a preferred period of time being nearer the shorter end of the range, or about five minutes, so as to reduce the time and cost needed to form the anti-friction or lubricious overcoat 145 during manufacturing. In general, a single application of the overcoat can be sufficient to form the lubricious overcoat 145 on top of the self-protective undercoat 143. However, multiple applications are also possible and considered to fall within the scope of the present disclosure.

Additional details for the selection of the substrate material 142 for the sealing sleeve 140, as well as the formation of the undercoat layer 143 comprising a self-protective oxide coating and the formation of the low-friction overcoat layer 145, can be found in co-owned and co-pending U.S. patent application Ser. No. 14/175,286, filed Feb. 7, 2014, and claiming priority to U.S. Provisional Patent Application No. 61/761,726, filed Feb. 7, 2013, which applications are incorporated by reference for all purposes in their entirety herein.

FIGS. 7 and 8 are cross-sectional side views of the high temperature slip joint 150 of FIG. 3, and illustrate the sealing sleeve 140 disposed between inner or male cylindrical surface 124 of the tubular attachment end 122 of the first section and the outer or female cylindrical surface 136 of the bore 134 formed into the tubular attachment end 132 of the second section. As can be seen, the alternating peaks 146 of the sealing sleeve 140 can provide multiple circumferential lines of contact 149 that allow the inner cylindrical surface 124 and the outer cylindrical surface 136 to slide relative to each other and to the sealing sleeve 140 while still restricting the passage of gases through the seal on either side of the sealing sleeve 140.

As further indicated in FIG. 6, the sealing sleeve 140 can be provided with a non-flexed distance or amplitude 147 between adjacent and opposite circumferential lines of contact 149 that is between about 6% and about 14% greater than an average gap distance between the opposed coaxial surfaces 124, 136, as measured perpendicular to a longitudinal axis of the tubular body. In one aspect the non-flexed distance or amplitude 147 of the wave-shaped sealing sleeve 140 can be about 10% greater than the average distance between the opposed coaxial surfaces 124, 136. Thus, as may be appreciated by one of skill in the art, installing the sealing sleeve 140 into the slip joint 150 (FIGS. 7-8) can cause the metallic tubular body or substrate 142 to compress, bend, or elastically deform to a smaller amplitude, and thereby generate a reactive or preload force that maintains the alternating peaks 146 of the sealing sleeve 140 firmly in contacted with the opposed co-axial surfaces 124, 136. In one aspect the preload force can be sufficient to maintain the sealing lines of contact 149 around the circumference of the slip joint 150 with a lateral or radial misalignment offset 125 (FIG. 4) that is equal to or about 3% of the average gap distance between opposed coaxial surfaces 124, 136. In another aspect the preload force can be sufficient to maintain the sealing lines of contact around the circumference of the slip joint 150 with an angular misalignment offset 135 (FIG. 4) that is equal to or about 0.5 degrees.

Another representative embodiment of the sealing sleeve 260 for a slip joint is illustrated in FIGS. 9-12, and generally comprises a tubular body or substrate 262 formed from a metallic material and having a first rolled end 264, a second rolled end 268, a center section 266 between the first and second rolled ends, and a longitudinal cross-sectional profile (FIGS. 10-11) having two bendable curves or arcs 270 that can open inwardly toward the center section 266. In one aspect the two inwardly-opening and circular arcs can be described as providing the cross-sectional profile of the sealing sleeve 260 with a Double-C shape.

Upon installation within the annular gap of the slip joint 250, as shown in the close-up views of FIGS. 11-12, opposite sides of both circular arcs 270 can contact the opposed coaxial surfaces 224, 236 so as to form two circumferential lines of contact 279 with each opposed coaxial surface, with the lines of contact 279 being separated by the width of the center section 266. Both the inner or male cylindrical surface 224 and the outer or female cylindrical surface 236 generally have substantially smooth surface finishes so that the arcs 270 of the sealing sleeve 260 can form substantially continuous lines of contact 279 around the entire circumference of the sealing sleeve. As described above, the multiple circumferential lines of contact 279 can allow the inner cylindrical surface 224 and the outer cylindrical surface 236 to move relative to each other and to the sleeve 260 while still restricting the passage of gases through the seal on either side of the sleeve 260.

As shown in FIG. 12, the circular arcs 270 can have an arc length 272 that ranges between about 220 degrees to about 270 degrees, and in one aspect can be about 254 degrees, as shown in the illustrated embodiment. In this configuration, the portion of the arc between the point of inflection 274 (i.e. where the arc 270 joins the radius of the curve that connects to the center section 266) and the vertical reference 276 (i.e. the line extending through the two lines of contact 279) can be about 21 degrees, and the portion of the arc between the vertical reference 276 and the tip 278 of the arc can be about 53 degrees. These dimensions can provide both of the arcs 270 with a desired degree of bendability or compressibility that allows the arcs 270 to roll or curl into themselves during insertion into the annular gap between the opposed coaxial surfaces 224, 236 of the slip joint 250 to reduce their diameter while maintaining their substantially circular shape.

Also shown in FIGS. 11-12, the center section 266 of the sealing sleeve 260 can include an offset 269 from the nearest slip joint surface, in this case the inner or male cylindrical surface 224, by at least about 10% of the average distance between the opposed coaxial surfaces 224, 236 upon installation of the sleeve 260 into the annular gap of the slip joint 250. The offset 269 of the center section 266 from the slip joint surface 224 can be advantageous to ensure that a reactive or preload force is substantially equal in all directions, including inwardly toward the center of the slip joint 250 as well as outwardly away from the slip joint.

The tubular body or substrate 262 of the sealing sleeve 260 can be formed from a stiff but bendable metallic material, such as a stainless steel alloy, an Inconel alloy, and a high-nickel alloy, that maintains its material properties at high temperatures. The substrate 262 can include an outer surface, an inner surface, and curled edges at the tips 278 of both arcs 270, and can be seamless or formed with a seamless construction. In one aspect substantially all of the surface area of the substrate 262, including both the outer and inner surfaces and the curled edges, can be covered with the undercoat layer 263 that provides the metallic material of the substrate 262 with protection from oxidation corrosion at high temperatures (FIG. 12). As described above, the undercoat layer 263 can be a self-protective oxide coating formed through the application of a plurality of nanoparticles to the surfaces of the substrate 262, which is then heated to a predetermined elevated temperature and for a predetermined period of time to form the self-protective oxide coating 263.

After the formation of the undercoat layer 263, a low-friction overcoat layer 265 can be applied to the undercoat layer 263 to provide lubricity to the contact surfaces 279 of the sealing sleeve 260 even when the sealing sleeve 260 is exposed to the elevated temperatures experienced by the exhaust manifold, which can often reach and exceed 600° C. In another aspect, the low-friction overcoat layer 625 can comprise boron nitride which can be applied in liquid form and allowed to dry.

As indicated in FIG. 10, the sleeve 260 can be provided with a non-flexed distance or arc diameter 267 between opposing circumferential lines of contact 279.

The non-flexed arc diameter 267 can be between about 6% and about 14% greater than an average distance between the opposed coaxial surfaces 224, 236 of the slip joint 250, as measured perpendicular to a longitudinal axis of the tubular body. In one aspect the non-flexed arc diameter 167 can be about 10% greater than the average distance between the opposed coaxial surfaces 224, 236.

Installation of the sealing sleeve 260 into the slip joint 250, as shown in FIGS. 13-16, generally causes the arcs 270 to compress, bend, or curl into themselves into smaller diameters as they roll or slide along the beveled edges 227, 237 formed into the leading surfaces of the tubular attachment ends 222, 232. This can cause the stressed metallic material of the substrate 262 to generate a reactive or preload force that maintains the opposing lines of contact 279 on each arc 270 firmly in contact with the opposed co-axial surfaces 224, 236. In one aspect the preload force can be sufficient to maintain the sealing lines of contact 279 around the circumference of the slip joint 250 with a lateral or radial misalignment offset 125 (FIG. 4) that is equal to or about 8% of the average gap distance between opposed coaxial surfaces 224, 236. In another aspect the preload force can be sufficient to maintain the sealing lines of contact 279 around the circumference of the slip joint 250 with an angular misalignment offset 135 (FIG. 4) that is equal to or about 1.2 degrees.

In one embodiment the non-flexed distance or arc diameter 167 (FIG. 10) can extend beyond the dimensions of both of the opposed coaxial surfaces 224, 236 of the slip joint 250 by equal amounts. In other words, the inside diameter 261 (FIG. 9) of the sleeve 260 between the inner contact surfaces 279 of the arcs 270 can be less than the outer diameter of the inner or male cylindrical surface 224 by about 5% of the average distance between the opposed coaxial surfaces 224, 236. Likewise, the outer diameter of the sleeve 260 (not marked) between the outer contact surfaces 279 of the arcs 270 can be greater than the inner diameter of the outer or female cylindrical surface 236 by about 5% of the average distance between the opposed coaxial surfaces 224, 236. In this way the reactive or preload forces generated by the compressed arcs 270 after insertion into the annular gap can be substantially equally distributed around the circumference of the slip joint 250.

The invention has been described in terms of preferred embodiments and methodologies considered by the inventors to represent the best mode of carrying out the invention. Nevertheless, it is contemplated that a wide variety of additions, deletions, and modification might well be made to the illustrated embodiments by those of skill in the art without departing from the spirit and scope of the invention, which is constrained only by the following claims. 

What is claimed is:
 1. A sleeve for sealing an annular gap between opposed co-axial surfaces of a slip joint, the sleeve comprising: a tubular body formed from a metallic material and having a first end, a second end, a center section between the first and second ends, and a longitudinal cross-sectional profile having a plurality of bendable curves, with at last two bendable curves contacting each opposed coaxial surface to form at least two circumferential lines of contact with each opposed coaxial surface; an undercoat layer comprising a self-protective oxide coating and covering substantially all of the surface area of the tubular body; and an overcoat layer covering the undercoat layer at least about the lines of contact and configured to provide lubricity to the contact surfaces when the sleeve is exposed to temperatures greater than about 600° C., wherein a non-flexed distance between opposing circumferential lines of contact is between about 6% and about 14% greater than an average distance between the opposed coaxial surfaces, as measured perpendicular to a longitudinal axis of the tubular body.
 2. The sleeve of claim 1, wherein the plurality of bendable curves further comprise a first rolled end and a second rolled end, the first and second rolled ends forming inwardly opposing arcs, each having an arc length greater than or about 230 degrees to provide the circumferential lines of contact with each opposed coaxial surface.
 3. The sleeve of claim 2, wherein the center section is spaced from a nearest slip joint surface by at least about 10% of the average distance between the opposed coaxial surfaces upon installation of the sleeve into the annular gap.
 4. The sleeve of claim 2, wherein the non-flexed distance further comprises a non-flexed diameter of the arcs as measured between opposed contact surfaces.
 5. The sleeve of claim 1, wherein the plurality of bendable curves further comprise a plurality of alternating peaks together forming a wave-shaped profile within the center section.
 6. The sleeve of claim 5, wherein the non-flexed distance further comprises a non-flexed amplitude as measured between the outer contact surfaces of adjacent peaks.
 7. The sleeve of claim 1, wherein the metallic material is selected from the group consisting of a stainless steel alloy, an Inconel alloy, and a high-nickel alloy.
 8. The sleeve of claim 1, wherein the self-protective oxide coating is formed from a plurality of nanoparticles applied to the surface and heated to a first elevated temperature and for a predetermined period of time to form the self-protective oxide coating.
 9. The sleeve of claim 8, wherein the plurality of nanoparticles are selected from the group consisting of cerium oxide nanoparticles, titanium oxide nanoparticles, aluminum oxide nanoparticles, silicon oxide nanoparticles, scandium oxide nanoparticles, yttrium oxide nanoparticles, zirconium oxide nanoparticles, niobium oxide nanoparticles, hafnium oxide nanoparticles, tantalum oxide nanoparticles, and thorium oxide nanoparticles.
 10. The sleeve of claim 1, wherein the overcoat layer comprises boron nitride.
 11. The sleeve of claim 1, wherein the tubular body is seamless.
 12. A sleeve for sealing an annular gap between opposed co-axial surfaces of a slip joint, the sleeve comprising: a tubular body having a first rolled end, a second rolled end, and a center section between the first and second rolled ends; the first and second rolled ends forming inwardly opposing arcs, each arc having an arc length greater than or about 230 degrees to form circumferential lines of contact with each opposed coaxial surface, and a diameter in a non-flexed condition that is at least about 10% greater than an average distance between the opposed coaxial surfaces; and the center section being spaced from a nearest slip joint surface by at least about 10% of the average distance between the opposed coaxial surfaces upon installation of the sleeve into the annular gap.
 13. The sleeve of claim 12, wherein the tubular body further comprises: a substrate formed from a metallic material and having an upper surface and a lower surface; an undercoat layer covering substantially all of the surface area of at least one of the upper surface and the lower surface, the undercoat layer comprising a self-protective oxide coating; and an overcoat layer on the undercoat layer and configured to provide lubricity to the surface when the sleeve is exposed to temperatures greater than about 600° C.
 14. The sleeve of claim 13, wherein the metallic material is selected from the group consisting of a stainless steel alloy, an Inconel alloy, and a high-nickel alloy.
 15. The sleeve of claim 13, wherein the self-protective oxide coating is formed from a plurality of nanoparticles applied to the surface and heated to a first elevated temperature and for a predetermined period of time to form the self-protective oxide coating.
 16. The sleeve of claim 13, wherein the overcoat layer comprises boron nitride.
 17. A sleeve for sealing an annular gap between opposed co-axial surfaces of a slip joint, the sleeve comprising: a tubular body formed from a metallic material and having a first end, a second end, and a center section between the first and second ends, the center section including a bendable wave-shaped profile formed from a plurality of alternating peaks contacting the opposed co-axial surfaces, with at least two peaks contacting each opposed coaxial surface to form at least two circumferential lines of contact with each opposed coaxial surface; an undercoat layer covering substantially all of the surface area of the tubular body, the undercoat layer comprising a self-protective oxide coating; and an overcoat layer covering the undercoat layer at least on each of the peaks of the wave-shaped profile and configured to provide lubricity to the surface when the sleeve is exposed to temperatures greater than about 600° C., wherein a non-flexed amplitude as measured between the lines of contact of adjacent opposing peaks is at least about 10% greater than an average distance between the opposed coaxial surfaces.
 18. The sleeve of claim 17, wherein the metallic material is selected from the group consisting of a stainless steel alloy material, an Inconel alloy material, and a high-nickel alloy material.
 19. The sleeve of claim 17, wherein the self-protective oxide coating is formed from a plurality of nanoparticles applied to the surface and heated to a first elevated temperature and for a predetermined period of time to form the self-protective oxide coating.
 20. The sleeve of claim 17, wherein the overcoat layer comprises boron nitride. 